TrainerRoad is amazing. It doesn't quite have a game feel to it, but it brings the suffer level of trainer workouts up while keeping you occupied with maintaining your power levels...
Oh yeah, and did I mention that all you need is an ANT+ Speed/Cadence sensor and an ANT+ USB stick to train with power on TrainerRoad?
That's right, for about $40 to $50 initial investment, you can train with power...that's an awesome deal.